Chip substrate for reducing thermal load on a chip assembly mounted thereon

ABSTRACT

A chip substrate includes a base substrate having a plurality of base circuit traces mounted thereon for supporting a chip assembly and an intermediate substrate mounted on the base substrate adjacent the plurality of base circuit traces. The intermediate substrate has a plurality of intermediate circuit traces mounted thereon. Each of the plurality of intermediate circuit traces are wirebonded to a respective one of the plurality of base circuit traces and the plurality of intermediate circuit traces are configured to be electrically coupled to an external device. For example, each of the plurality of intermediate circuit traces may be wirebonded to a respective one of a plurality of feedthrough circuit traces mounted on a feedthrough device.

TECHNICAL FIELD

The present disclosure relates generally to chip assemblies and moreparticularly to devices and methods for reducing thermal load on chipassemblies mounted thereon.

BACKGROUND

Chip assemblies (e.g., sensor chip assemblies) typically experiencethermal load transfer from an external device to which a detector of thechip assembly is electrically connected. For example, with reference toFIG. 1, a hermetically sealed dewar container 10 housing a chip assembly12 (e.g., a sensor chip assembly) under a vacuum is depicted. Afeedthrough device 14 is provided to electrically couple the chipassembly 12 within the vacuum to an external device (not pictured)outside of the vacuum. While the junction of the feedthrough device 14and a housing of the dewar container 10 is hermetically sealed, so as tomaintain the vacuum within the dewar container 10, the wirebondconnection between the feedthrough device 14 and a substrate 16 of thechip assembly 12 provides a path for thermal load transfer between theexternal device and a detector 18 of the chip assembly 12 inside thedewar container 10. Specifically, with reference to FIG. 2, thesubstrate 16 includes a plurality of substrate circuit traces 17 whichare each wirebonded to a respective one of a plurality of feedthroughcircuit traces 19.

Such thermal load transfer to the chip assembly 12 may be detrimental tothe performance of the detector 18. Therefore, it is important tomitigate such thermal load transfer to the chip assembly 12. Existingapproaches to help mitigate thermal load transfer to the chip assembly12 include providing a cooling source (not pictured) within the dewarcontainer 10, such as in the cooling chamber 20 depicted in FIG. 1, tohelp cool the chip assembly 12 mounted above the cooling chamber 20.However, in some instances, the size and thermal capacity of suchcooling source must be large to sufficiently mitigate the thermal loadtransfer between the external device and the chip assembly.

SUMMARY

In a general embodiment, a modified chip substrate (e.g., a sensor chipsubstrate) of a chip assembly (e.g., a sensor chip assembly) isconfigured to reduce the thermal load transfer from an external deviceto the chip assembly. The chip substrate includes a base substrate andan intermediate substrate mounted on the base substrate. The basesubstrate includes a plurality of base circuit traces and theintermediate substrate includes a plurality of intermediate circuittraces each wirebonded to a respective one of the plurality of basecircuit traces. The plurality of intermediate circuit traces areconfigured to be electrically coupled to an external device so as toelectrically couple the external device to the chip assembly. Forexample, a feedthrough device having a plurality of feedthrough circuittraces may be provided and each of the plurality of intermediate circuittraces may be wirebonded to a respective one of the plurality offeedthrough circuit traces. The feedthrough device, therefore, may beelectrically coupled to the external device and may serve toelectrically couple the external device to the chip assembly.

According to an aspect of this disclosure, therefore, a chip substrateincludes a base substrate having a plurality of base circuit tracesmounted thereon for supporting a chip assembly. The chip assembly alsoincludes an intermediate substrate mounted on the base substrateadjacent the plurality of base circuit traces. The intermediatesubstrate has a plurality of intermediate circuit traces mountedthereon. Each of the plurality of intermediate circuit traces arewirebonded to a respective one of the plurality of base circuit traces.The plurality of intermediate circuit traces are therefore configured tobe electrically coupled to an external device.

According to an embodiment of any paragraph(s) of this summary, amaterial of the base substrate has a first thermal conductivity and amaterial of the intermediate substrate has a second thermal conductivitythat is lower than the first thermal conductivity.

According to another embodiment of any paragraph(s) of this summary, thesecond thermal conductivity lower than the first thermal conductivity bya factor that is within an order of magnitude of 50.

According to another embodiment of any paragraph(s) of this summary, thematerial of the base substrate is any one of aluminate (AlO₂) andaluminum nitride (AlN).

According to another embodiment of any paragraph(s) of this summary, thematerial of the intermediate substrate is at least one of steatite,yttria, forsterite, cordierite, and zirconia.

According to another embodiment of any paragraph(s) of this summary, theplurality of intermediate circuit traces are each wirebonded to arespective one of the plurality of base circuit traces with a respectivegold wirebond.

According to another embodiment of any paragraph(s) of this summary, theplurality of intermediate circuit traces are each wirebonded to arespective one of the plurality of base circuit traces with a respectivesilver wirebond.

According to another embodiment of any paragraph(s) of this summary, theplurality of base circuit traces and the plurality of intermediatecircuit traces are made of gold.

According to another embodiment of any paragraph(s) of this summary, atleast a portion of the intermediate substrate is spaced apart from thebase substrate with a gap between the portion of the intermediatesubstrate and the base substrate.

According to another aspect of this disclosure, a chip substrateassembly includes a chip substrate having a base substrate. The basesubstrate has a plurality of base circuit traces mounted thereon forsupporting a chip assembly. The chip substrate also includes anintermediate substrate mounted on the base substrate adjacent theplurality of base circuit traces. The intermediate substrate has aplurality of intermediate circuit traces mounted thereon. Each of theplurality of intermediate circuit traces are wirebonded to a respectiveone of the plurality of base circuit traces. The chip substrate assemblyalso includes a feedthrough device having a plurality of feedthroughcircuit traces mounted thereon. Each of the plurality of feedthroughcircuit traces are wirebonded to a respective one of the plurality ofintermediate circuit traces.

According to another aspect of this disclosure, a method of electricallycoupling a chip assembly mounted on a base substrate to an externaldevice includes the step of mounting an intermediate substrate on thebase substrate adjacent a plurality of base circuit traces mounted onthe base substrate. The intermediate substrate includes a plurality ofintermediate circuit traces mounted thereon. The method also includesthe step of wirebonding each of the plurality of intermediate circuittraces to a respective one of the plurality of base circuit traces, andelectrically coupling each of the plurality of intermediate circuittraces to the external device.

According to an embodiment of any paragraph(s) of this summary, the stepof electrically coupling each of the plurality of intermediate circuittraces to the external device includes the steps of providing afeedthrough device having a plurality of feedthrough circuit tracesmounted thereon, and wirebonding each of the plurality of feedthroughcircuit traces to a respective one of the plurality of intermediatecircuit traces on the intermediate substrate.

According to another embodiment of any paragraph(s) of this summary, thestep of wirebonding each of the plurality of intermediate circuit tracesto a respective one of the plurality of base circuit traces includeswirebonding each of the plurality of intermediate circuit traces to arespective one of the plurality of base circuit traces with a respectivegold wirebond.

According to another embodiment of any paragraph(s) of this summary, thestep of wirebonding each of the plurality of intermediate circuit tracesto a respective one of the plurality of base circuit traces includeswirebonding each of the plurality of intermediate circuit traces to arespective one of the plurality of base circuit traces with a respectivesilver wirebond.

According to another embodiment of any paragraph(s) of this summary, thestep of mounting the intermediate substrate on the base substrateincludes spacing at least a portion of the intermediate substrate apartfrom the base substrate such that a gap is provided between the portionof the intermediate substrate and the base substrate.

The following description and the annexed drawings set forth in detailcertain illustrative embodiments of this disclosure. These embodimentsare indicative, however, of but a few of the various ways in which theprinciples of this disclosure may be employed. Other objects, advantagesand novel features of this disclosure will become apparent from thefollowing detailed description of this disclosure when considered inconjunction with the drawings.

BRIEF DESCRIPTION OF DRAWINGS

The annexed drawings show various aspects of this disclosure.

FIG. 1 is a cross-sectional perspective view of a conventional dewarcontainer housing a conventional chip assembly.

FIG. 2 is a perspective view of a conventional chip substrate assemblyof the conventional chip assembly depicted in FIG. 1

FIG. 3 is a perspective view of a chip substrate assembly.

FIG. 4 is a perspective view of another chip substrate assembly.

FIG. 5 is a flowchart of a method of electrically coupling a chipassembly mounted on a base substrate to an external device, according toanother aspect of this disclosure.

DETAILED DESCRIPTION

According to a general embodiment, a chip substrate of a chip assemblyincludes a base substrate and an intermediate substrate. Unlikeconventional chip substrates, which do not include an intermediatesubstrate mounted on a base substrate, the chip substrate reducesthermal load transfer from an external device to the chip assembly ascompared to conventional chip substrates (FIG. 2). For example, withreference to FIG. 3, a substrate assembly 22 (e.g., a sensor chipsubstrate assembly) including a substrate 24 (e.g. a sensor chipsubstrate) is depicted. The chip substrate 24 includes a base substrate26 and an intermediate substrate 28. The chip substrate 24 may be housedin a hermetically sealed dewar container, like that of FIG. 1, so as tobe held under a vacuum. At least one of the base substrate 26 and theintermediate substrate 28 may be a 1024K×1024K substrate with a unitcell size in the range of 2 micrometers to 60 micrometers, 3 micrometersto 50 micrometers, 4 micrometers to 30 micrometers, 5 micrometers to 25micrometers, or 8 micrometers to 16 micrometers.

The base substrate 26 includes a plurality of base circuit traces 30.Each of the plurality of base circuit traces 30 may have a size in therange of 0.001 inch (0.025 millimeter) to 0.100 inch (2.54 millimeter),0.002 inch (0.05 millimeter) to 0.05 inch (1.27 millimeter), 0.003 inch(0.08 millimeter) to 0.04 inch (1.02 millimeter), 0.004 inch (0.10millimeter) to 0.03 inch (0.76 millimeter), 0.005 inch (0.13 millimeter)to 0.02 inch (0.51 millimeter), or 0.007 inch (0.178 millimeter) to 0.01inch (0.25 millimeter). The base circuit traces 30 are configured to beelectrically coupled to a chip assembly (e.g., a sensor chip assembly;not pictured) mounted on the chip substrate 24. As a non-limitingexample, the base circuit traces 30 may be made of gold. It isunderstood, however, that other materials may be used for the basecircuit traces 30, such as for example silver.

The intermediate substrate 28 of the chip substrate 24 includes aplurality of intermediate circuit traces 32. The intermediate circuittraces 32 are configured to be electrically coupled to the basesubstrate 26. Specifically, each of the plurality of intermediatecircuit traces 32 are wirebonded to a respective one of the plurality ofbase circuit traces 30. As a non-limiting example, the intermediatecircuit traces 32 may be made of gold. Each of the plurality ofintermediate circuit traces 32 may be wirebonded to a respective one ofthe plurality of base circuit traces 30 with, for example, a gold orsilver wirebond. It is understood, however, that other materials may beused for the intermediate circuit traces 32 and the wirebondelectrically coupling the intermediate circuit traces 32 to the basecircuit traces 30, such as for example silver, copper, aluminum, or anycombination thereof.

The intermediate circuit traces 32 are also configured to beelectrically coupled to an external device (not pictured) so as toelectrically couple the external device to the chip assembly mounted onand electrically coupled to the chip substrate 24. As mentioned above,the chip substrate 24 may be housed in a hermetically sealed dewarcontainer, like that of FIG. 1, so as to be held under a vacuum.Accordingly, as depicted in FIG. 3, the substrate assembly 22 mayinclude a feedthrough device 34 configured to extend through a housingof the dewar container and electrically couple the chip substrate 24under the vacuum to an external device outside of the vacuum. In thisway, the feedthrough device 34 is configured to electrically couple theexternal device to the chip assembly mounted on the chip substrate 24under the vacuum. The feedthrough device 34, therefore, may include aplurality of feedthrough circuit traces 36 on or near a first end 38thereof, and may include pins 40 for electrically coupling the externaldevice on or near a second end 42 thereof. The plurality of feedthroughcircuit traces 36 on or near the first end 38 of the feedthrough device34 may be housed and hermetically sealed within the dewar containerunder the vacuum along with the chip substrate 24 so as to beelectrically coupled to the chip substrate 24 therein. Specifically,each of the plurality of feedthrough circuit traces 36 may be wirebondedto a respective one of the plurality of intermediate circuit traces 32on the intermediate substrate 28 of the chip substrate 24. The pins 40on or near the second end 42 of the feedthrough device 34 may beprovided on an outside of the hermetically sealed dewar container suchthat the pins 40 may be electrically coupled to the external device. Thefeedthrough device 34 may include a seal ring 44 disposed around aperiphery of the feedthrough device 34 for providing a hermetic sealbetween the feedthrough device 34 and a housing of the dewar container.

The chip substrate 24 disclosed herein reduces the thermal load transferbetween the external device, and/or feedthrough device, and the chipassembly mounted on the chip substrate 24 by the addition of theintermediate substrate 28. That is, the intermediate substrate 24 mayhave a lower conductivity than the base substrate 26, reducing thethermal load transfer therethrough. Specifically, a material of the basesubstrate 26 may have a first thermal conductivity and a material of theintermediate substrate 28 may have a second thermal conductivity that islower than the first thermal conductivity. For example, the secondthermal conductivity of the material of the intermediate substrate 28may be lower than the first thermal conductivity of the material of thebase substrate 26 by a factor of about 50 or within an order ofmagnitude of 50, such as from 5 to 500, from 10 to 250, from 25 to 100,or from 40 to 60. The material of the base substrate may be any one ofaluminate (AlO₂) and aluminum nitride (AlN). The material of theintermediate substrate 28 may be any one of steatite, yttria,forsterite, cordierite, and zirconia, or any suitable combinationthereof. It is understood, however, that the listed materials of thebase substrate 26 and the intermediate substrate 28 are provided asnon-limiting examples and that other suitable materials may be appliedto the base substrate 26 and the intermediate substrate 28 in accordancewith this disclosure, such as for example titanium porcelain.

With reference to FIG. 4, at least a portion 46 of the intermediatesubstrate 26 may be spaced apart from the base substrate 28 with a gap48 disposed between the portion 46 of the intermediate substrate and thebase substrate 28. This configuration further reduces the thermal loadtransfer between the external device, and/or the feedthrough device 34,and the chip assembly mounted on the chip substrate 24. That is, as airhas a generally low thermal conductivity (especially at the low pressureunder the vacuum within the hermetically sealed dewar container),providing the gap 48 in the path of the thermal load transfer, thethermal load on the chip substrate 24 may be further reduced. Theportion 46 of the intermediate substrate 26 may be located anywhere onthe intermediate substrate 26 and the gap 48 may have any shape or sizerelative to the intermediate substrate 26.

The substrate assembly 22 disclosed herein is capable of reducing thethermal load by approximately 50% as compared to conventional chipsubstrates. In this manner, the chip substrate assembly 22 allows forfaster cool-down times of the chip assembly and a detector thereof. Thechip substrate assembly 22 also allows for reduced size and thermalcapacity of alternative cooling sources.

With reference to FIG. 5, a method 100 of electrically coupling a chipassembly (e.g., a sensor chip assembly) mounted on a base substrate toan external device is depicted. The chip assembly, for example, may bemounted on the base substrate 28 of the substrate assembly 24 describedabove (FIGS. 3 and 4). The method therefore includes the step 102 ofmounting an intermediate substrate, such as the intermediate substrate26 (FIGS. 3 and 4), on the base substrate adjacent a plurality of basecircuit traces, such as the base circuit traces 30 (FIGS. 3 and 4),mounted on the base substrate. The step 102 of mounting the intermediatesubstrate may include spacing at least a portion of the intermediatesubstrate apart from the base substrate such that a gap, such as the gap48 described above (FIG. 4), is provided between the portion of theintermediate substrate and the base substrate. The intermediatesubstrate includes a plurality of intermediate circuit traces, such asthe intermediate circuit traces 32 (FIGS. 3 and 4). The method thenincludes the step 104 of wirebonding each of the plurality ofintermediate circuit traces to a respective one of the plurality of basecircuit traces. Such wirebonding serves to electrically couple each ofthe plurality of intermediate circuit traces to a respective one of theplurality of base circuit traces. The method 100 then includes the step106 of electrically coupling each of the plurality of intermediatecircuit traces to the external device.

For example, the step 106 of electrically coupling each of the pluralityof intermediate circuit traces to the external device may include thesteps of providing a feedthrough device, such as the feedthrough device34 (FIGS. 3 and 4) described above. The feedthrough device has aplurality of feedthrough circuit traces mounted thereon. The step 106 ofelectrically coupling each of the plurality of intermediate circuittraces to the external device may then include the step of wirebondingeach of the plurality of feedthrough circuit traces to a respective oneof the plurality of intermediate circuit traces on the intermediatesubstrate. The step of wirebonding each of the plurality of intermediatecircuit traces to a respective one of the plurality of base circuittraces may include wirebonding each of the plurality of intermediatecircuit traces to a respective one of the plurality of base circuittraces with a respective gold or silver wirebond. Such wirebondingserves to electrically couple each of the plurality of feedthroughcircuit traces to a respective one of the plurality of intermediatecircuit traces on the intermediate substrate. In this manner, theexternal device electrically coupled to the feedthrough device maytherefore be electrically coupled to the chip assembly mounted on thebase substrate of the substrate assembly.

Although this disclosure has been shown and described with respect to acertain preferred embodiment or embodiments, it is obvious thatequivalent alterations and modifications will occur to others skilled inthe art upon the reading and understanding of this specification and theannexed drawings. In particular regard to the various functionsperformed by the above described elements (components, assemblies,devices, compositions, etc.), the terms (including a reference to a“means”) used to describe such elements are intended to correspond,unless otherwise indicated, to any element which performs the specifiedfunction of the described element (i.e., that is functionallyequivalent), even though not structurally equivalent to the disclosedstructure which performs the function in the herein illustratedexemplary embodiment or embodiments of this disclosure. In addition,while a particular feature of this disclosure may have been describedabove with respect to only one or more of several illustratedembodiments, such feature may be combined with one or more otherfeatures of the other embodiments, as may be desired and advantageousfor any given or particular application.

1. A substrate, comprising: a base substrate having a plurality of basecircuit traces mounted thereon for supporting a chip assembly; and anintermediate substrate mounted on the base substrate adjacent theplurality of base circuit traces, the intermediate substrate having aplurality of intermediate circuit traces mounted thereon, each of theplurality of intermediate circuit traces being wirebonded to arespective one of the plurality of base circuit traces; wherein theplurality of intermediate circuit traces are configured to beelectrically coupled to an external device.
 2. The substrate accordingto claim 1, wherein a material of the base substrate has a first thermalconductivity and a material of the intermediate substrate has a secondthermal conductivity that is lower than the first thermal conductivity.3. The substrate according to claim 2, wherein the second thermalconductivity is lower than the first thermal conductivity by a factorthat is within an order of magnitude of
 50. 4. The substrate of claim 1,wherein the material of the base substrate is any one of aluminate(AlO2) and aluminum nitride (AlN).
 5. The substrate of claim 1, whereinthe material of the intermediate substrate is at least one of steatite,yttria, forsterite, cordierite, and zirconia.
 6. The substrate of claim1, wherein the plurality of intermediate circuit traces are eachwirebonded to a respective one of the plurality of base circuit traceswith a respective gold wirebond.
 7. The substrate of claim 1, whereinthe plurality of intermediate circuit traces are each wirebonded to arespective one of the plurality of base circuit traces with a respectivesilver wirebond.
 8. The substrate of claim 1, wherein the plurality ofbase circuit traces and the plurality of intermediate circuit traces aremade of gold.
 9. The substrate of claim 1, wherein at least a portion ofthe intermediate substrate is spaced apart from the base substrate witha gap between the portion of the intermediate substrate and the basesubstrate.
 10. A substrate assembly, comprising: a substrate including:a base substrate having a plurality of base circuit traces mountedthereon for supporting a chip assembly; and an intermediate substratemounted on the base substrate adjacent the plurality of base circuittraces, the intermediate substrate having a plurality of intermediatecircuit traces mounted thereon, each of the plurality of intermediatecircuit traces being wirebonded to a respective one of the plurality ofbase circuit traces; and a feedthrough device having a plurality offeedthrough circuit traces mounted thereon, each of the plurality offeedthrough circuit traces being wirebonded to a respective one of theplurality of intermediate circuit traces.
 11. A method of electricallycoupling a chip assembly mounted on a base substrate to an externaldevice, the method comprising the steps of: mounting an intermediatesubstrate on the base substrate adjacent a plurality of base circuittraces mounted on the base substrate, the intermediate substrateincluding a plurality of intermediate circuit traces mounted thereon;wirebonding each of the plurality of intermediate circuit traces to arespective one of the plurality of base circuit traces; and electricallycoupling each of the plurality of intermediate circuit traces to theexternal device.
 12. The method according to claim 11, wherein the stepof electrically coupling each of the plurality of intermediate circuittraces to the external device includes the steps of: providing afeedthrough device having a plurality of feedthrough circuit tracesmounted thereon; and wirebonding each of the plurality of feedthroughcircuit traces to a respective one of the plurality of intermediatecircuit traces on the intermediate substrate.
 13. The method accordingto claim 11, wherein a material of the base substrate has a firstthermal conductivity and a material of the intermediate substrate has asecond thermal conductivity that is lower than the first thermalconductivity.
 14. The method according to claim 13, wherein the secondthermal conductivity is lower than the first thermal conductivity by afactor that is within an order of magnitude of
 50. 15. The methodaccording to claim 11, wherein the material of the base substrate is anyone of aluminate (AlO2) and aluminum nitride (AlN).
 16. The methodaccording to claim 11, wherein the material of the intermediatesubstrate is at least one of steatite, yttria, forsterite, cordierite,and zirconia.
 17. The method according to claim 11, wherein the step ofwirebonding each of the plurality of intermediate circuit traces to arespective one of the plurality of base circuit traces includeswirebonding each of the plurality of intermediate circuit traces to arespective one of the plurality of base circuit traces with a respectivegold wirebond.
 18. The method according to claim 11, wherein the step ofwirebonding each of the plurality of intermediate circuit traces to arespective one of the plurality of base circuit traces includeswirebonding each of the plurality of intermediate circuit traces to arespective one of the plurality of base circuit traces with a respectivesilver wirebond.
 19. The method according to claim 11, wherein theplurality of base circuit traces and the plurality of intermediatecircuit traces are made of gold.
 20. The method according to claim 11,wherein the step of mounting the intermediate substrate on the basesubstrate includes spacing at least a portion of the intermediatesubstrate apart from the base substrate such that a gap is providedbetween the portion of the intermediate substrate and the basesubstrate.